Wireless communication has evolved into a world of multi-standards/multi-services with operating frequencies of 900 MHz/1.8 GHz/1.9 GHz bands for GSM, 1.5 GHz band for GPS and 2.4 GHz/5.2 GHz/5.7 GHz bands for WLAN. Therefore, it is desirable to combine two or more standards in one mobile unit. The primary challenge in designing multi-band transceivers is increasing the functionality of such communication systems while minimizing the number of additional hardware such as low noise amplifiers (LNAs). Typical design strategies have used different LNAs for different frequency bands. However, this inevitably increases cost, power consumptions and form-factor. In other words, to design a three-band transceiver using the frequency bands of 0.9 GHz, 1.8 GHz, and 1.9 GHz, three different low-noise amplifiers must be designed to cope with the three different frequency bands. Therefore, the relevant gains, noise figures, input impedances, and output impedances are all designed for the specific frequency band when a low-noise amplifier is designed. Therefore, the form factor and power consumption of the multi-band transceiver are much greater than the single-band transceiver. As an example, please refer to the integrated multi-band super-heterodyne receiver of the prior art as shown in FIG. 1. From the antenna 100, through the frequency band selection filter 101 (102 is a bandpass filter), the low-noise amplifier 103, the images rejection filter 104 (105 is a bandpass filter), the mixer having an input of the local oscillator signal 106, and the channel selection filter 107 (108 is a bandpass filter), all of which form the independent receiving route of the first application frequency band. From the antenna 109, through the frequency band selection filter 110 (111 is a bandpass filter), the low-noise amplifier 112, the images rejection filter 113 (114 is a bandpass filter), the mixer having an input of the local oscillator signal 115, and the channel selection filter 116 (117 is a bandpass filter), all of which form the independent receiving route of the second application frequency band. From the antenna 118, through the frequency band selection filter 119 (120 is a bandpass filter), the low-noise amplifier 121, the images rejection filter 122 (123 is a bandpass filter), the mixer having an input of the local oscillator signal 124, and the channel selection filter 125 (126 is a bandpass filter), all of which form the independent receiving route of the third application frequency band.
Using the independent receiving route of the first application frequency band as an example, signals will be received by the antenna 100 firstly. These received signals will go through a frequency band selection filter 101 so as to filter out the signals outside the desired frequency band secondly. Signals fall within the desired band will go into the low-noise amplifier 103 to be amplified and to avoid the increasing of noises thirdly. The amplified signals will go through an image rejection filter 104 to delete the noises generated by the image frequencies. After finishing the down-conversion, a channel of the first application frequency band is selected by the channel selection filter 107. A common portion of the above-mentioned circuit shared by the first independent route, the second independent route, and the third independent route, which includes the mixer 127, the analog-digital converter 128, and the digital signal processor 129, is connected to the channel selection filter 107. If a signal is confirmed belonging to an application band, it is down-converted and is digitized by the analog-digital converter 128. Finally, the digitized signals are processed in the digital signal processor 129.
From the above description, the traditional way of integrating a multi-band receiver is to design the circuit applicable to each frequency band separately and to combine all these circuits together. The critical circuits in the receiver, the low-noise amplifiers, have to be designed one for each different frequency band too. Thus the form factor and the power consumption of the whole circuit are increased dramatically. In the prior art, this is the method employed to integrate a circuit applicable to the multi frequency band (that is, to employ a different amplifier to handle each of the different frequency band).
Please refer to the following references:
    a. S. Wu and B. Razavi, “A 900-MHZ/1.8-GHz CMOS receiver for dual-band applications,” IEEE JSSC, pp. 2178-2185, December 1998;    b. R. Magoon, et. al, “A triple-band 900/1800/1900 MHz low-power image-reject front-end for GSM,” ISSCC Digest of Technical papers, pp. 408-409, February 2001;    c. K, L, Fong “Dual-band high-linearity variable-gain low-noise amplifiers for wireless applications,” ISSCC Digest of Technical papers, February 1999.
Recently, a designing method regarding using the same low-noise amplifier to process all of the multi-band signals has been proposed by H. Hashemi and A. Hajimiri as described in the paper “Concurrent multiband low-noise amplifiers-theory, design, and applications,” IEEE Transactions on Microwave Theory and Techniques, pp. 288-301, 2002. Since the same low-noise amplifier can be employed to fulfill the requirements of all the different frequency bands, the design of the transceiver for the integration of multi-band applications can be simplified (no need to design multiple low-noise amplifiers). Both the form factor and the power consumption of the whole circuit can be decreased which is quite advantageous to the merchandizing of the circuit.
The above-mentioned designing method proposed by H. Hashemi and A. Hajimiri is different from the traditional designing method for the low-noise amplifiers. As for the traditional designing method for the low-noise amplifiers in the prior art, please refer to FIG. 2. The source inductor 207 is employed to generate the resistance desired for the input impedance matching (usually 50 ohm). The inductor 201 is also employed to achieve a resonance at the desired frequency band with the total input capacitance looking into the gate. At the output terminal, resonant LC tank formed by the inductor 204 and the capacitor 208 is employed to choose the desired frequency band.
As for the designing method for the multi-band low-noise amplifiers proposed by H. Hashemi and A. Hajimiri, please refer to FIG. 3. In addition to the inductor 310 for generating the resistance needed by the input impedance matching at the input terminal (usually 50 ohm) and the inductor 304 for achieving the resonance at the desired frequency band are employed as in the prior art, the capacitor 302 and the inductor 301 electrically connected in parallel are also employed. The purpose of doing this is to add another resonant frequency to acquire the function of multi-band input impedance matching. In addition to the resonant LC tank including the inductor 312 and the capacitor 313 connected in parallel at the output terminal is employed as in the prior art, inductor 307 and capacitor 306 connected in parallel are also employed. The purpose of doing this is also to add another resonant frequency to acquire the function of selecting the desired frequency band among the given multi-bands. In other words, through increasing the number of inductors and capacitors to acquire the functions regarding the multi-band applications is employed by H. Hashemi and A. Hajimiri. A designing method like this has many disadvantages, which are described as follows.
Firstly, five inductors (that is inductors 301, 304, 307, 310, and 312, wherein inductors 301 and 304 are not on the chip) and three capacitors (the capacitors 302, 306, and 313 are included, in which the capacitor 302 is not on the chip) are employed in this design with two extra inductors and two extra capacitors compared to the traditional design of the low-noise amplifier (please refer to FIG. 2, in which there are three inductors: 201, 204, and 207 and one capacitor 208). Because the number of the inductors and the capacitors are increased and off-chip inductors and capacitor are employed (square measures of which are much greater than those on the chip), the form factor of the whole circuit is increased dramatically, and such a design cannot be fabricated on a single chip. Besides, the off-chip inductors and capacitor would need extra jobs of wire-bonding and wiring, which will increase the cost and decrease the reliability, and hence are not facilitate to the mass-producing and merchandizing of the ICs. Usually, when a low-noise amplifier is designed, the circuit designers try to use as few inductors as possible for the reasons given below. Firstly, the inductors will occupy a lot of precious chip area. Secondly, the quality factors of the inductors on the chips are not high, which will degrade the noise figures. That is why the utilization of the inductors is avoided as much as possible when a low-noise amplifier is designed. However, the method proposed by H. Hashemi and A. Hajimiri increases the utilization of the inductors instead.
That is why a new kind of multi-band amplifiers, which will not increase the form factor and the number of elements of the whole circuit, and will not require extra jobs of wire-bonding and wiring, are really in need.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the designing methods and circuits for multi-band electronic circuits are finally conceived by the applicants.